The use of silicon nitride films for microelectronic applications is at present the focus of considerable research. Silicon nitride has been proposed as a substitute for SiO.sub.2 as an insulating or masking or passivating layer. Its advantages over SiO.sub.2 are:
1. higher dielectric constant PA0 2. imperviousness to the diffusion of impurities PA0 3. greater resistance to contamination PA0 4. reduction in threshold voltage.
Many methods have been applied for producing silicon nitride films. These include direct nitridation of silicon by thermal treatment with a nitrogen containing gas, chemical vapor deposition, evaporation, sputtering and glow discharge processes. For each of the above methods, pattern definition is typically accomplished through optical lithography.
The obvious advantage of ion beam techniques over optical lithography is the ability to directly write lines and patterns on a substrate. In the manufacture of integrated circuit (IC) devices, the photolithographic and associated processes are in many cases the limiting factor to good yields. It is thus apparent that it may be advantageous to use alternative methods such as ion beam techniques. Additionally, it is anticipated that charged beam techniques (e.g. electron and ion) will provide the resolution necessary to meet the demand for the ever increasing miniaturization of circuit geometries as required in VLSI applications.
Previous attempts to produce silicon nitride with the use of ion beams have focused on implantation of N.sup.+ or N.sub.2 .sup.+ into a silicon substrate. The films synthesized by these methods have in general showed a deficiency in nitrogen relative to stoichiometric Si.sub.3 N.sub.4. This may explain the inferior electrical characteristics of silicon nitride formed by ion implantation compared to chemical vapor deposited Si.sub.3 N.sub.4.
It is accordingly an object of the invention to provide an alternative method which may be used in lieu of prior art methods that suffer from the above and other deficiencies.